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Guest cfm562

Runway Overrun at SEQU and Autobrakes

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OK, so last night, just messing around, not taking things so seriously as to calculate weight vs. landing distance etc. I flew from SKBO to SEQU in the 747X (Which I must say to PMDG is the most brilliantly designed aircraft ever made for FS ..THANKS)Anyhow, taking off from SKBO with 1/3 fuel thinking weight might be a consideration at higher altitudes and such I lined up on the ILS for 35 and with autobrakes set to max and flaps to 25 with an approach speed of 174. (Now in retrospect I probably should have used 30 flaps and opted for that 8 knot reduction) I touched down on the 12,000 foot runway on full autoland just after the threshold and got 1/3 the way down the runway, with reversers and speedbrakes when it seemed the autobrakes just weren't working. Maybe they were, maybe I just panicked or something and I slammed on the brakes and just still went off the end into some guy's house. Yeah, it was bad, ugly in fact, went sliding down a big hill and everything. It totally reminded me of the A340 accident at SEQU on Nov 9. So a couple of questions, because despite some obvious failure to do a complete flight plan, it still was annoying to me. So, can anyone else verify any autobrake issues? If there is a post on that already im sorry, I also just wanted to share. Is the field elevation of 9000 feet affecting stopping distance? I would assume reverser effectiveness is less, but it only stops thrust mostly anyway.They say that an A340 is the biggest a/c allowed into SEQU, but they aren't that dramatically different in size. I would have thought with 1/3 fuel, full autobrakes, reversers, spoilers, I would have got her stopped in 12,000 feet (Minus the displaced threshold of course). I've got a mind to repeat the flight later with full flaps and a 168 aproach speed, and then manually slamming on the brakes at touchdown, see if I can get it in without making a 747 nosewheel a permanent part of somebody's living room.Any thoughts?Shane Lewis

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Shane,A couple of factors...you say 1/3 fuel...is that 1/3 of approx 170t?...thats possibly 70t of gas...how long was the flight?(distance)...Bogota-Quito would require considerably less fuel than 70t!!! ZFW...how much payload were you carrying?Its sounds like your landing weight may have been at near maximum...I fly the 744F into Quito regularly from KMIA & plan on a fairly moderate payload (ZFW 235-245t)coupled with approx 15t of gas remaining...giving me a planned landing weight in the region of 250-260t.At Quito I use VREF +10, FLAP 30, Autobrake 3 & FULL REV down to 80kts...with no problems encountered.Regardles of any issue you may have with the Autobrakes it sounds as if you may have been too heavy to make a successful landing anyway at an airport above 9000 AMSL.As for the Autobrake issue a quick forum search will reveal several posts on this issue...with the requisite solutions to the problem. Try a trial flight at a familiar airport under normal condidtions iot ascertain if your Autobrakes are functioning correctly.Hope this helps!!Kind RegardsSteve Bell

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Thanks Steve, I suspected I was probably overweight, and that flight is only 1.25 hrs. Payload set to 1/2 of max or so. I just thought that 12,000ft of runway would be enough. So, what are the real debilitating factors of landing at high altitudes with heavy weight. I totally get taking off, as the air is too thin to get max lift. That of course is a principal of high altitude flying. But on landing, I'm principally relying on the brakes to stop. The spoilers kill the lift on the wing to put the most amount of weight on the ground so that brakes can be effective. The diminished lift of high altitudes by my reasonings should be a benefit to braking performance. Reversers primarily redirect the exhaust flow as not to push the aircraft further forward. So by my reasoning, the primary force in stopping the aircraft is braking, then spoilers and airframe to provide air resistance, followed by some minimal forwardly directed reverse thrust. So my question is....How does high altitude adversely affect landing distance, unless reversers truly are THAT effective as engines rate less power at high altitudes.Oh and it's really nice to know that someone is bringing the plane into SEQU safely. Gonna do that flight again, and correctly this time. Thanks for your help!Shane Lewis

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Shane,Firstly...I'm not a RW pilot...so take what I say with a large pinch of salt!!!High Alt landing = thin air = higher landing speed = higher descent rate = longer stopping distance & I guess yes, the reversers will not produce the same performance due to the limiting conditions.Interstingly the RW RWY has a distinct 'crown' just past the midpoint...downhilll from there futher limiting RW performance.Kind RegardsSteve BellPS Having checked my notes I use VREF +10, FLAP 25 & Autobrake 3.

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Nice analysis Steve, like you I'm just trying to sort this in my head. It makes us better pilots for it. So lets see, I hadn't thought of the fact that the thinner air will produce a higher descent rate, so....that would explain the reason partially why the 747X slammed into the pavement at SEQU, do you notice less ground effect there? Is FS realy modelling this? That would be fascinating. Interestingly I really didn't get a Flare signal either....I wonder if that was by design at that airport as they want you on the ground as quickly as possible? Here's my thoughts though, and I'm not trying to belabor a point, I just have some honest questions in my head.My approach speed at most airports with 30 flaps is between 160 and 170 depending on winds I assume. With 25 flaps last night at SEQU, it was calculating 174 and with 30 it was 168 knots.So with that thought, 168 knots is ballpark for landing at any sea level airport as well from my Queen flying experience.You should reasonably be able to stop any 747 on 10,000 feet of runway with 1/3 fuel and a full payload at sea level right? So then, if you hit the pavement at 168 knots.....I would think performance would be comparable even at 9000 feet, as braking is concerned. Now that you mention it, there are three debilitating factors here.1. Engines will obviously produce less power at altitude, so what stopping force the reverse thrust does produce will be somewhat less. 2. Air resistance on the airframe will be less. hadn't thought of that, so rollout will be longer, but how much? Surely not 1000 feet longer?3. This downhill crown, certainly isn't affecting things positively.So does all of this combined produce such a more severely increased stopping distance?I guess my question comes down to this for you "heavy a/c-knowledged" people. Does altitude significantly reduce stopping effectiveness given all other factors the same?I really need to refly this flight on Steve's suggestions as my whole perception of that flight could be skewed given the careless way I executed the flight in the first place. (i.e. not even knowing my max landing weight)Are there any TOPCAT users that can verify that stopping distance is increased at altitude given all other variables the same? Thanks all,Shane Lewis

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Shane,I guess what I am tring to say (remember I'm not a RW pilot!!) is that the the thinner air makes the aircraft work harder...it will require a significantly higher groundspeed (& TAS) iot maintain the necessary pitch attitude required to maintain the glideslope. This higher GS & TAS will therefore result in a higher rate of decent on the glideslope profile.What do you mean by a 'Flare Signal'?...the higher rate of descent will therefore require a deeper flare commenced at a higher altitude above the RWY (increased pitch attitude) iot reduce the RoD to an acceptable level consumate with a landing within design limitations. I guess this is compounded by the reduction in aerodynamic performance in the thinner air. Looking at the Jepp SEQU VOR ILS Descent 7 Chart a GS of 160kts descending on the 3.2 degree glideslope will produce a RoD of 919FPM!Interestingly in the RW the G/S antenna is positioned almost a third of the way down the RWY...if the G/S signals are followed until touchdown the aircraft will probably land too far along the RWY (beyond the TDZ) iot make stopping probably impossible...instead if above the minima the AP is disconnected & then the PAPI is flown to the TDZ...that's straight from PPRuNE...so as John B says take that with a pinch of salt too!! I am not too sure if this antenna is positioned within FS as it is in the RW...but I will check.AFIK there is no Autoland, CAT 1,2 or 3 capability at Quito...the minima are as follows: DA(H) 9850 Baro (652 RA)Vis 4000mSo an Autoland is not permitted & I have doubts as to whether the aircraft is actually capable of doing such at this altitude...RW operators chime in here!!!There is no ballpark VREF for any given landing...it depends on many factors such as A/C LDG Weight, FLAP Selection, Weather, RNWY length/elev etc...I use TOPCAT religiously on every departure & landing...I recommend it to all 744/X users...GE & RR engine variants are available in addition to the F variant...its worth every penny/cent given in donation to the designer Christian Grill...PW engine variants are also on the way. Of course you should always compare this to the figures produced by the FMC.Lets now look at the TOPCAT data comparison between a landing at the same weight at a sea level airport (HKG) & Quito at 15'C, 1013mb & nil winds...747-400F at a landing weight of 265t, FLAP 25 & Autobrake 4:VHHH = RWY 25L 3800MVREF 154VAPP 159Actual LDG Dist - 1865MLDG Dist Avail - 3800MDist Rem - 1935MSEQU = RWY 35 3120MVREF 156VAPP 166Actual LDG Dist - 2639MLDG Dist Avail - 3035MDist Rem - 481MI deliberately added +5 kts to the Quito calculations to produce the VREF +10 figure as a safety margin. As I stated earlier a GS of 160 kts produces a RoD in excess of 900FPM!!!Not much difference in the VREF...this may be a limitation of TOPCAT...I am unable to find any RW 744 high altitude ldg data. But the stopping distance is dramatically different as you can see.AFIK runway slope is not modelled in FS9 or FSX...I was just referring to another issue with the RW RWY 34 at SEQU.As for the engine perfomance issues...I liken it to trying to run up a hill carrying a heavy rucksack...at sea level it will be fairly slow but manageable...try it at 9000 AMSL or higher (believe me I have!!) & you will find it much harder...now try the same running down & try & stop...its much harder the higher up you are...I guess this is my layman's attempt to understand what happens to engine performance at higher altitudes...just like my lungs they suffer from perfomance issues the higher AMSL they go.Hope this helps & its a nice change from some of the boring topics of late. If you fly online then please send me a PM...we can then organise a time to fly the KMIA-SEQU route online...ATC there loves seeing the 744...it can become a granstand event for some of the regular locals too...last time I did it I even got a compliment from one of them!!! - Great fun.RW operators please chime in if I am barking up the wrong trees!Kind RegardsSteve Bell

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Did you have the little red text that says brakes in the bottom left corner? If not then brakes = not working.Me, I can't get autobrakes to work 99% of the time and wait a few seconds and if they don't come on hit the brake pedals manually full. There are a few other threads about autobrakes not working but no one can say why not yet.John Veldthuishttp://www.virtualpilots.org/signatures/vpa475.png

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Wow Steve, I believe you have taught me some things here. Your data sure seems reasonable and it most definitely makes me rethink some things. excellent analysis here on TAS vs indicated. I think the point is that Indicated airspeed, (what we are flying based on the FMS) is going to be the same no matter what.....my error was in making the incorrect assumption that the IAS of the aircraft (ie (168 or 174 in the previous examples)translated to the same value at sea level as at SEQU. I see quite logically from your initial sentence that I am mistaken. Since IAS is measured using RAM air pressure in the pitot tube, it will take significantly more air (read:groundspeed) to generate 168kts on approach, which also translates to 168kts of airspeed over the wings. But since we must go faster to attain this speed, our groundspeed must increase, which translates to higher ROD because we must come down faster since we are travelling across the ground faster. Understood.Also fascinating is the fact that SEQU has a 12,000 ft runway, which is rarer to see at sea level, I guess we know why now.BTW, Flare signal is the signal on the MFD that says FLARE when it captures the flare signal from the ILS. This probably isn't present in approaches not Cat II or III approved. If present it automatically causes the a/c to flare and touchdown on landing. I'm sure you knew that though.Impressive Topcat numbers, wow, 800 extra feet due to that extra speed on touchdown. Gee, now I know what was missing last night. 800 extra feet! Yep that would have solved the problem. I am now fully convinced that autobrakes did not activate (No red brake indicator (thanks fellow in the next post)) which if I had been Johnny-on-the-spot on the brakes I might have still gotten it stopped.I completely agree with you on the engines, definitely going to be more laborious in every aspect, however, I still believe that the reverse thrust is minimal if not negligable in this scenario as Reversers really just cancel out forward thrust. I think the MD80's with their clamshell reversers actually can backup with reverse, but not the 744, but this may be weight/power related, but I tend to think it is more related to the way the reverser baffles cup around the high bypass ducts and blow the stream out the sides of the engine. Could be wrong.So then I think we have a clear answerHigher GS + Lower Wind Resistance + Reduced reverser effectiveness=800 Extra feet needed on touchdown (weight dependent of course). Makes sense to me, and now.......I can add that to my mental checklist for when landing at high altitudes. Never used TOPCAT before, looks like its gonna be a regular thing for me now.I used to fly alot online, particularly adjusted to SB3, but now that it isn't working with FSX, I am yet to try it online. FSINN seemed like a pain. Maybe I am not used to it yet. What software are you using for ATC? I sure would love to get back in my groove, lets plan on making that KMIA-SEQU trip, now if I can figure out how to PM. Don't knock yourself on not being a RW pilot, I supposedly went through all this training back in '87 for my PPL, Engine Performance for my A&P in '95, but it still takes some real world scenarios (or simulated) to make these more interesting topics understood. I mean lets face it, every flight manual taught Density Altitude and take-off performance. Its a no-brainer for any moderately trained Private pilot, but landing performance at 744 weights at the highest airports in the world?? Unless you are a heavy driver, we will never get this kind of training in real world unless you are fortunate enough to get to the heavies. I wonder, how many SWA pilots flying 73's, which all can stop in probably 8000 ft or less at max gross landing weight even cover being able to stop at ultra high altitudes in under 10,000 ft. Where would it apply for them? I don't think this would be even a problem for them in Denver, at gross weight (meaning not being able to stop at KDEN) . But, you sir, are on your game, RW pilot or not. My compliments.Thanks for the great discussion. Look forward to doing a few trips.Shane LewisKATL

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Steve,OK, Reflew the whole flight, SKBO-SEQUthis time leaving SKBO with 70K fuel and 2/3 payload. Arrived at 30K Fuel, 158kts approach 30 flaps, landed perfectly with 200 feet of runway to spare....but autobrakes of course didn't work. Amazing how much runway you use there. Amazing. Well, so that was it. Thanks alot for everything, much more satisfying. I sure learned something new today.Shane Lewis

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Shane,I IMHO still think you are landing with far too much fuel...but there you go!!!With reference to your Autobrake issue...I had the same problem a while back.My solution was to re-calibrate my CH Pro Pedals via the FSUIPC interface creating a larger 'null' or neutral zone. I suspect your pedals are creating 'spikes' of movement as you rest your feet on them...or the current setting that FSX is picking up is telling FSX that they are already being applied...this of course will cause the Autobrake to immediately disconnect on landing.Try a re-calibration & then a few test flights at somewhere you know well...it should solve your issues.I still use FS9 as my platform with WIN XP on my simming PC, with SB3 & WideClient for the online stuff running on my laptop via a wireless internet router (I have my mate Carl Avari-Cooper to thank for helping me set it all up!!).Hope this helpsSteve Bell

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